A QP analyzer filters the ions to pass the specified mass according to the applied voltage.

The figures show the top view and side view of a QP mass analyzer. You have a view of the ion's motion when the voltages are applied to pass the m/z 180 ion. Check the trajectories of ions by entering the m/z numbers into the box, for example m/z=180, 181, 179. You will find that only the m/z 180 ion can reach the exit of the rod, but other m/z ions go off course. Due to this behavior, a QP rod is sometimes called a mass filter.

Mass Filtering by QP Analyzer